1. Field of the Invention
This invention relates to purification of 1,1,1-trichloroethane that is contaminated with at least one undesirable C.sub.1 -C.sub.3 chlorocarbon, for example, 1,1-dichloroethane, 1,2-dichloroethane, cis-1,2-dichloroethylene or trichloroethylene. In particular, it relates to a process for the purification of 1,1,1-trichloroethane by contacting the impure 1,1,1-trichloroethane with a special adsorbent, the adsorbent being a particulate product of controlled pyrolysis of a polysulfonated macroporous crosslinked vinylaromatic polymer having a surface area of at least about 500 m.sup.2 /g, a micropore pore volume of at least about 0.24 ml/g, a macropore pore volume: of less than about 0.24 ml/g and a ratio of macropore to micropore pore volume of less than 100 percent.
2. Background of the Invention
Because 1,1,1-trichloroethane is usually produced by chlorination of ethane or ethyl chloride, the product is usually contaminated with undesirable C.sub.1 -C.sub.3 chlorocarbons such as 1,2-dichloroethane and trichloroethylene, which detract from the usefulness of the 1,1,1-trichloroethane produced. While various methods for the purification of 1,1,1-trichloroethane have been attempted, such methods have achieved only moderate success. For example, while removal of relatively large quantities of 1,2-dichloroethane has been accomplished by extractive distillation, the 1,2-dichloroethane levels in the 1,1,1-trichoroethane are reduced only to around 0.05 percent. Examples of such processes have been demonstrated by Leroi et al, Ger. Offen. DE 2,627,992 (20 Jan. 1977), by Boozalis et al, U.S. Pat. No. 3,989,601 (2 Nov. 1976) and by Gabler et al, Ger. Offen. DE 2,036,939 (3 Feb. 1972). Trichloroethylene is usually removed by ordinary distillation processes, but small residues remain unless a highly efficient distillation column is used. A further problem of various prior art processes is that decomposition of the 1,1,1-trichloroethane often results because of the heat applied or because of chemical reaction.
A number of these various prior processes for the purification of 1,1,1-trichloroethane are sufficient for many purposes, e.g., when the solvent is intended for use in degreasing. Such processes of purification, however, are inadequate for certain applications which require the use of 1,1,1-trichloroethane of very high purity. For example, when 1,1,1-trichloroethane is used as an intermediate for the synthesis of fluorohydrocarbons and chlorofluorohydrocarbons, much lower levels of both 1,2-dichloroethane and trichloroethylene are desired.
The present invention provides a process capable of reducing the levels of 1,1-dichloroethane, 1,2-dichloroethane, dichloroethylene and trichloroethylene to less than about 10 ppm, and even to less than about 1 ppm, without decomposition of 1,1,1-trichloroethane.
Various forms of activated carbon have been used to remove certain chlorocarbons and their mixtures from aqueous solutions, but not for the separation of the chlorocarbons from each other. An example of the use of carbon fibers for the recovery, but not separation, of various chlorocarbon solvents is disclosed in Satake, et al, Kagaku Sochi, 30(3), 93-7 (Japan) 1988 (Chem. Abs. 109:95073 g).
In view of the limited success of prior art purification processes for 1,1,1-trichloroethane, there thus exists a long felt need in the art for a process for the purification of 1,1,1-trichloroethane which will reduce the concentration of undesirable chlorocarbons to an art-accepted level without decomposition of the desired product. There is also a need in the art for a purification process that is capable of separating the removed chlorocarbons from each other.